Re: [CAD_CAM_EDM_DRO] PIC DRO stupid question

Hi,

I've tried playing with this and its a non-starter. You run into three
problems - one:- the printer doesn't seem accurate enough to print close
lines to a great degree of accuracy. I tried both an HP 890C Deskjet and a
laser printer and tried printing the lines both horizontally and vertically.
Whilst they come out very close, there is a noticeable discrepancy when you
try to overlay two identical printouts. Second:- it is almost impossible to
get a dense enough print to be of any practical use, in fact, probably the
only way to achieve this would be to produce the scales on lithographic film
which is an entirely different process. Third:- if you are using deskjet
film, it has a granular coating to retain the ink which gives the print
fuzzy edges and would rub off if you slid two films together as you would
have to to make a working detector.
I have been considering several possibilities for making gratings but
haven't come up with anything workable yet. One of the most recent was
wrapping two lengths of fine wire closely around a glass or plastic rod and
then removing one of them, so leaving a regularly spaced coil on a light
guide. This ought to work but the round wire gives problems with light
scatter around its edges.

Ian

--
Ian W. Wright
Sheffield UK

----- Original Message -----
From: Wayne Bengtsson <wbbengtsson@...>
To: <CAD_CAM_EDM_DRO@egroups.com>
Sent: 07 April 2000 10:21
Subject: RE: [CAD_CAM_EDM_DRO] PIC DRO stupid question


>
> -----Original Message-----
> From: Jon Elson [mailto:jmelson@...]
> Sent: Friday, 7 April 2000 1:58 AM
>
> >Really, if someone can come up with accurate grating patterns on film or
> >glass, it is fairly
> >easy to make your own linear encoder. Does anyone have any ideas on
> >where to get
> >such grating patterns?
>
> One quick and easy way to make such a pattern would be to draw the pattern
> in a good CAD program, and print the pattern on to transparency material
> using the best quality injet printer you have access to.